1. Field of the Invention
The present invention relates to tintable coating compositions, and more particularly to a tintable coating compositions made from an admixture of a carboxylated urethane polymer mixture made from 1,6-hexanediol and 4,4-methylenebis(cyclohexylisocyanate); a hydroxylated methylmethacrylate acrylic polymer; an aziridine-based cross-linking agent; and an optional solvent.
2. Description of the Related Art
Increasingly stringent environmental regulations are gradually phasing out organic solvent-based paints, coatings, and adhesives in favor of those using more innocuous solvents, such as water. Water-based polymer coating components are becoming increasingly available to impart unique characteristics to metal surfaces, such as color, gloss, adhesive layers, corrosion protection, mar and wear resistance, and the like. However, such water-based polymer coatings have not performed as well as their organic solvent-based counterparts in terms of hardness, gloss, durability, and other characteristics that are demanded from the marketplace. Consequently, there is continuing development in the area of water-based polymer coatings that perform as well as organic solvent-based polymer coatings, yet are not damaging to the environment.
U.S. Pat. No. 5,118,752 discloses aqueous polymerization of vinyl monomers, including acrylates, in the presence of a polymeric surfactant containing urethane groups and silane groups.
U.S. Pat. No. 5,141,983 discloses an aqueous coating composition comprising an aqueous polyurethane resin and an aqueous dispersion of an acrylic copolymer, and an aqueous coating composition obtained by polymerizing radical-polymerizable acrylic monomers in the presence of an aqueous urethane resin.
U.S. Pat. No. 5,204,404 discloses a water-based coating composition containing an acrylic silane polymer and a polyurethane polymer. Similarly, U.S. Pat. No. 5,286,569 also discloses a water-based coating composition containing an acrylic silane polymer and a polyurethane polymer.
U.S. Pat. No. 5,739,194 discloses an aqueous dispersion of urethane and vinyl polymers that make up a water-based coating composition.
While these coating materials may be satisfactory for certain applications, there is still need for improved tintable coating compositions that have properties such as color or decoration, gloss, mar-, wear-, and moisture-resistance, strong adhesion to the substrate, the like, yet are water-based and safe for the environment. The present invention is believed to be an answer to that need.
In one aspect, the present invention is directed to a tintable coating composition, comprising an admixture of: (A) about 2 to about 80 wt % of a carboxylated urethane polymer dispersion mixture made from 1,6-hexanediol and 4,4-methylenebis(cyclohexylisocyanate); (B) about 5 to about 65 wt % of a hydroxylated methylmethacrylate acrylic polymer emulsion; (C) about 0.1 to about 3 wt % of a crosslinking agent, the crosslinking agent comprising an aziridine-based crosslinking compound; and (D) optionally, about 0.5 wt % to about 25 wt % of a solvent; all percentages based on the total weight of the coating composition.
In another aspect, the present invention is directed to a tintable coating composition, comprising an admixture of: (A) about 2 to about 80 wt % of a carboxylated urethane polymer mixture made from 1,6-hexanediol and 4,4-methylenebis(cyclohexylisocyanate), wherein the carboxylated urethane polymer mixture comprises a mixture of a about 2 to about 75 wt % of a first carboxylated urethane polymer made from 1,6-hexanediol and 4,4-methylenebis(cyclohexylisocyanate), and having an acid number of about 36, and about 5 to about 80 wt % of a second carboxylated urethane polymer made from 1,6-hexanediol and 4,4-methylenebis(cyclohexylisocyanate), and having an acid number of about 28; (B) about 5 to about 65 wt % of a hydroxylated methylmethacrylate acrylic polymer emulsion; (C) about 0.1 to about 3 wt % of a crosslinking agent, the crosslinking agent comprising an aziridine-based crosslinking compound; (D) about 5 to about 40 wt % a decorative component selected from the group consisting of dyes, metal flakes, metal powders, glass flakes, glass powders, and combinations thereof; (E) about 0.005 to about 2 wt % of one or more additives selected from the group consisting of surfactants, defoamers, and combinations thereof; and (F) optionally, about 0.5 wt % to about 25 wt % of a solvent selected from the group consisting of water, N-methylpyrrolidone, butylcarbitol, 2-butoxyethanol, isopropyl alcohol, and combinations thereof; all percentages based on the total weight of the coating composition.
In yet another aspect, the present invention is directed to substrates coated with the above tintable coating compositions.
These and other aspects will be more fully understood from the following detailed description of the invention.
It has now been found, in accordance with the present invention, that an admixture of (1) about 2 to about 80 wt % of a carboxylated urethane polymer dispersion mixture made from 1,6-hexanediol and 4,4-methylenebis(cyclohexylisocyanate); (B) about 5 to about 65 wt % of a hydroxylated methylmethacrylate acrylic polymer emulsion; and (C) about 0.1 to about 3 wt % of a crosslinker comprising an aziridine-based crosslinking agent forms a water-based coating composition that possesses excellent hardness, durability, and wear-resistance. The coating composition of the invention has a low VOC (volatile organic content) and can be pigmented with many existing commercial pigments or other decorative additives to form xe2x80x9ctintedxe2x80x9dcoatings. The composition has excellent adhesion to a variety of substrates such as aluminum, copper, stainless steel, cold rolled steel, phosphatized steel, steel coated with conventional primers such as electrodeposition primers and the like, plastic substrates such as polyester reinforced fiber glass, injection molded urethanes, polystyrenes, and polyimides. A clear coat can be applied to a layer of the tinted composition to provide a clear/color coat finish. The coating composition used for the clear coat can be the coating composition of this invention or another compatible aqueous or solvent based coating composition.
As used herein, the term xe2x80x9ctintablexe2x80x9d refers broadly to the presence of a decorative component in the composition of the present invention, such as a colorant, dye, pigment, metal flake or powder, or glass flake or powder, or other decorative component, to provide the coating composition with color or other decorative effect. The term xe2x80x9cdispersionxe2x80x9d, as used herein, refers generally to a two-phase system where one phase consists of finely divided particles distributed throughout a bulk substance (usually a solvent). The term xe2x80x9cemulsionxe2x80x9d refers to a stable mixture of two or more immiscible liquids held in suspension by small amounts of emulsifiers.
As mentioned above, the invention is a tintable coating composition, comprising an admixture containing primarily (A) a carboxylated urethane polymer dispersion mixture made from 1,6-hexanediol, and 4,4-methylenebis(cyclohexylisocyanate); (B) a hydroxylated methylmethacrylate acrylic polymer emulsion; (C) a crosslinking agent that comprises an aziridine-based crosslinking compound; and (D) optionally, a solvent. Each of these components is discussed in more detail below.
The carboxylated urethane polymer dispersion component of the present composition is a dispersion made from a combination of 1,6-hexanediol and 4,4-methylenebis(cyclohexylisocyanate). The solvent portion of the dispersion may be water, or a combination of water and water-miscible or water-immiscible organic solvents. A preferred material is sold under the trade name QW 18-1 (available commercially from SIA Polymers, Inc., Seabrook, NH) and has an acid number of about 36. When cured, this particular product, by itself, has a sword hardness of about 25. Another preferred material having a similar combination of ingredients is sold under the tradename QW 26 (also available commercially from SIA Polymers), and has an acid number of about 28. When cured, this particular product, by itself, has a sword hardness of about 40.
In the composition of the present invention, the preferred products QW 18-1 and QW 26 may be used individually or in combination. Generally, the total amount of carboxylated urethane polymer is preferably in the range from about 2 wt % to about 80 wt %, based on the total weight of the composition. In one embodiment, a combination of QW 18-1 and QW 26 is used in which QW 18-1 is present in the composition in the range of from about 2 to about 75 wt %, based on the total weight of the composition, and QW 26 is present in the composition in the range of from about 5 to about 80 wt %, based on the total weight of the composition. A more preferred combination is made from between about 15 wt % and about 25 wt % of QW 18-1, and about 20 wt % to about 30 wt % of QW 26, all based on the total weight of the composition. A particularly preferred amount of carboxylated urethane polymer is about 26 wt % QW 26, and about 18.8 wt % QW 18-1. Additional specifically preferred combinations are summarized in the Examples below.
The hydroxylated methylmethacrylate acrylic polymer component of the present invention is preferably a product sold as an aqueous emulsion under the tradename xe2x80x9cMAINCOTE AE58xe2x80x9d by Rohm and Haas Corporation, and has a glass transition temperature (Tg) of +50xc2x0 C. Preferably, this component of the composition of the invention is present in the range between about 5 wt % and 65 wt %, and more preferably between about 30 wt % and 40 wt %, based on the total weight of the composition. A particularly preferred amount of hydroxylated methylmethacrylate acrylic polymer emulsion is 34 wt %.
The crosslinking agent of the present invention includes an aziridine-based crosslinking compound. As defined herein, the term xe2x80x9caziridine-based crosslinking compoundxe2x80x9d refers to compounds such as polymers that include at least two aziridine moieties wherein the aziridine moieties are positioned in the molecule such that they are each capable of reacting with other polymers. Suitable aziridine-based crosslinking compounds that include two aziridine moieties have the general Formula I: 
where R is any linking polymer of any length. For example, R may be 3-50 carbon atoms in length, or may include branched carbon chains or other functional groups.
Although Formula I shows an aziridine-based crosslinking compound with two aziridine moieties positioned on each end, greater numbers of aziridine moieties may be present in the molecule, for example three, four, five, or more. One particularly useful aziridine-based crosslinking compound includes three aziridine moieties and has the structure shown in Formula II: 
This compound is available from Sybro Chemicals, Inc. (Birmingham, N.J.) and sold under the tradename IONAC XAMA-7.
As defined herein, the term xe2x80x9ccrosslinking agentxe2x80x9d refers to the aziridine-based crosslinking compound either alone or in combination with other known crosslinking compounds and/or solvents. One particularly useful family of additional crosslinking compounds is the epoxylated silane crosslinking compounds, for example, glycidoxypropyltrimethoxy silane, and related compounds. Glycidoxypropyltrimethoxy silane is available commercially from Dow Corning and is sold under product number Z6040. Other useful crosslinking agents include carbodiimide and zirconium dioxide dispersion.
The crosslinking agent component of the invention preferably ranges from about 0.1 wt % to about 3 wt %, and more preferably between about 1 and 2 wt %, based on the total weight of the composition. A particularly useful amount of crosslinking agent is 1.0 wt %. If a combination of aziridine-based crosslinking compound and other crosslinking compounds is used, the aziridine-based crosslinking component preferably comprises no less than 40 wt % of the crosslinking agent, and the other crosslinking compounds preferably comprise no more than 60% by weight of the crosslinking agent. For example, in one embodiment, the crosslinking agent may be made from between about 90% and about 40% by weight of aziridine-based crosslinking compound, and from about 10% to about 60% by weight of glycidoxypropyltrimethoxysilane, all percentages based on the total weight of the crosslinking agent. In another exemplary embodiment, the crosslinking agent may be made from between about 75% and about 50% by weight of aziridine-based crosslinking compound, and between about 25% and about 50% of glycidoxypropyltrimethoxysilane, all percentages based on the total weight of the crosslinking agent.
It should be understood that the amount of crosslinking agent used in any particular application will depend on the length of time the crosslinking agent has been in contact with the other components of the composition, and the desired degree of crosslinking required for the composition. With respect to the age of the crosslinking agent, it is known that some crosslinking agents react with water and lose their effectiveness over time. Therefore, one skilled in the art can easily adjust the amount of cross-linking agent in any particular composition of the invention to account for this phenomenon. Also, one of skill in the art can adjust the amount of crosslinking agent to obtain a desired degree of crosslinking. It is possible to increase the stability of the cross-linking agent by adjusting and maintaining the pH of the coating solution above 7.0 with a base, and preferably within the range of from 7.0 to 9.5, and more preferably between 8.5 and 9.5. Without wishing to be bound by any particular theory, it is believed that the aziridine-based crosslinking compound produces crosslinking in the coating which is responsible for the excellent durability, mar- and wear-resistance, as well as its outstanding chemical and moisture resistance properties.
Optionally, additional solvent may be added to the coating composition of the invention to achieve a specific viscosity for applications such as spraying, or to achieve a certain dry/cure time. Suitable solvents include water, combinations of water and water-miscible or water-immiscible organic solvents, or water-miscible or water-immiscible organic solvents. Useful solvents include water, N-methylpyrrolidone, butylcarbitol, 2-butoxyethanol, various alcohols, such as isopropyl alcohol, and the like. Suitable combinations of these solvents may also be employed in the composition of the present invention. Useful amounts of these solvents range from 0.5 to 25 wt %, based on the total amount of the coating composition.
The coating composition of the present invention may be used as a clear coat, or may include a decorative component, such as a colorant dye, pigment, metal flake or powder, or glass flake or powder, to provide the coating composition with color or other decorative effect. Particularly useful decorative additions to the composition of the present invention are inks that impart a color to the coating composition. A variety of suitable inks are available commercially from Tech Ink Inc. (Akron, Ohio). In one embodiment, the coating composition of the invention includes a red ink such as red ink number A-3701 from Tech Ink, Inc. Generally, the decorative component of the invention is present in amounts ranging from about 5 to about 40 wt %, and more preferably from about 15 to 20 wt %, based on the total weight of the composition, depending on coating thickness and color/decorative tone desired.
The water-based coating composition of the invention may include other ingredients that enhance the adhesion of the composition to the substrate, or that aid in it""s application to the substrate. Such additional additives include, but are not limited to, film-forming solvents, defoamers, surfactants, and combinations thereof. Preferably, these additional additives comprise, it total, between about 0.005 to about 2 wt % of the composition.
2-Butoxyethanol may be added to the coating composition of the invention as a film-forming agent. The film-forming agent is added to the composition to provide a smooth coating surface for maximum coating area. Alternative film-forming agents include N-methylpyrrolidone, diethylene glycol, or other organic solvents known in the art that have boiling points higher than that of water. Preferably, the film-forming agent is present in the composition from about 0 to about 1% by weight of the total composition, and more preferably, from about 0.0005 to about 0.015% by weight of the total composition.
A defoaming agent may be included in the coating composition of the invention to prevent air entrapment during processing and to provide a smooth coating surface that provides maximum surface area for adhesion. Exemplary defoaming agents include siloxane-based defoaming agents such as Dow Corning #62, silicon oils, mineral oils, modified alcohol ethoxylates, EO/PO block copolymers (repeating units of ethoxy and propoxy groups), phosphate esters, hydrophobic silica, and fatty alcohols as well as blends of these. Other defoaming agents include copolymers of EO/PO sold under the trademark xe2x80x9cBASF PLURONICSxe2x80x9d, alkoxylated straight chain alcohols sold under the trademark xe2x80x9cPLURFACSxe2x80x9d; alkoxylated fatty acids, alcohols, or glycols sold under the trademark xe2x80x9cANTAROXxe2x80x9d alkoxylated alcohols and block copolymers of EO/PO sold under the trademark xe2x80x9cMACOLxe2x80x9d; alkylphenol alkoxylates sold under the trademark xe2x80x9cTRITON CFxe2x80x9d; alkoxylated alcohols sold under the trademark xe2x80x9cTRITON DFxe2x80x9d; alkylated secondary alcohols sold under the trademark xe2x80x9cTERGITOLxe2x80x9d, xe2x80x9cMINIFOAMxe2x80x9d, xe2x80x9c15Sxe2x80x9d and xe2x80x9cTMNxe2x80x9d; and alkoxylated linear alcohols and glycols sold under the trademark xe2x80x9cSURFONICxe2x80x9d. The defoaming agent preferably comprises about 0 to about 1% by weight of the total composition, and more preferably 0.00125 to about 0.0125% by weight of the total composition. A particularly useful defoaming agent is a polyether modified dimethylsiloxane, such as Dow Corning additive #62 (available from Dow Corning), and a particularly useful amount is about 0.005 wt %, based on the total amount of the coating composition.
A surfactant may be added to the coating composition of the invention to aid in leveling the composition on the substrate as it is applied. One preferred type of surfactant useful in the coating composition of the invention are the silicon-based surfactants, such as xe2x80x9cSILWETxe2x80x9d (Witco Chemical Co.). Another exemplary surfactant useful in the composition of the invention includes poly(oxyethylene/oxypropylene) alkyl ethers sold under the trademark xe2x80x9cPOLYTERGENTxe2x80x9d. Alternatively, nonionic surfactants which are block copolymers of ethylene oxide/propylene oxide monomers may be used in the formulation of the invention. These compounds are known commercially as the xe2x80x9cPOLYTERGENTxe2x80x9d P and E Series and are available from Olin Corporation. Particularly useful surfactants are the hydroxylated dimethylsiloxanes, such as Dow Corning Q2-5211 available from Dow Corning. Preferably, the surfactant component is present in the composition from about 0 to about 1 percent by weight of the total composition, and more preferably from about 0.00125 to about 0.05% by weight of the total composition. A particularly useful amount of surfactant is 0.025 wt %, based on the total weight of the coating composition.
The coating composition of the present invention is prepared by mixing the carboxylated urethane polymer dispersion mixture, the hydroxylated methylmethacrylate acrylic polymer emulsion, the aziridine-based cross-linking agent, and any additional components such as dyes, colorants, decorative flakes, defoamers, surfactants, solvents, and the like, in a commercial mixer, such as a Ross mixer. The entire mixture is blended until a smooth and homogeneous coating composition is obtained.
The prepared coating composition may be applied to a variety of substrates such as stainless steel, aluminum, copper, iron, cold rolled steel, phosphatized steel, steel coated with conventional primers such as electrodeposition primers and the like, plastic substrates such as polyester reinforced fiber glass, injection molded urethanes, polystyrenes, polyimides, and the like. In some cases, the substrate should be cleaned prior to coating with the composition of the invention to assure good adhesion and durability.
The composition of the invention may be applied to the selected substrate by any method known in the art, such as draw down rod, doctor blading, gravure roll, spraying, dipping, and the like. Preferably, the coating composition of the invention is applied to the substrate at about 0.2 to 0.4 mil wet thickness, and is cured in an oven at a temperature between 150xc2x0 C. and 300xc2x0 C. for 15 seconds to about 20 minutes. A preferred cure procedure is heating in a convection oven set to about 250xc2x0 C. and exposing the coated substrate to that temperature for about 1-2 minutes. The thickness of the dried coating is generally in the range of from about 0.1 to about 0.2 mil.
The water-based coating composition of the invention possesses excellent hardness, durability, wear-, mar-, and moisture-resistance. The coating composition of the invention also has a low VOC (volatile organic content), excellent substrate adhesion, and is suitable for many applications, such as automotive paints, clear coats, and the like, where durability and long adhesion life are required. The composition of the present invention also possesses low VOC content (about 1.8 lbs/gallon (minus water) and about 0.88 lbs/gallon including water) making it an environmentally innocuous product.
The following Examples are provided to better illustrate the present invention. All parts and percentages are by weight and all temperatures are degrees Celsius, unless explicitly stated otherwise.